1. Anionic type: Hydrophilic groups are negatively charged, such as sulfates (e.g., sodium dodecyl sulfate, SDS), sulfonates (sodium dodecylbenzenesulfonate). Known for their strong cleaning power and rich lather, they are relatively more irritating and were key components in soaps and early detergents.
2. Cationic type: Hydrophilic groups are positively charged, primarily consisting of quaternary ammonium salts (such as benzalkonium chloride). They are characterized by strong bactericidal properties but are generally incompatible with anionic surfactants and exhibit relatively high irritation. They are commonly used in disinfectants and hair conditioners (where they neutralize the negative charge of hair to provide antistatic effects).
3. Zwitterionic type: The molecule contains both positive and negative charges simultaneously, such as in the betaine type (R-N+(CH3)2-COO-) and amino acid types. They are characterized by extremely low irritation, good tolerance to hard water, and excellent compatibility. Depending on pH conditions, they can exhibit either anionic or cationic properties, and are often used as a co-surfactant to reduce the irritation of formulations.
4. Non-ionic type: Hydrophilic heads are non-ionic, such as fatty acid glycerides, sucrose esters, and alkyl glycosides (APG), fatty alcohol polyoxyethylene ether (AEO), etc. It is characterized by being mild, low-foaming, and highly stable, with its performance significantly affected by temperature (exhibiting a cloud point phenomenon). It is widely used in high-end facial cleansers, lotions, and industrial additives.
In nanomedicine (such as drug delivery systems and nanomaterials), surfactants play an indispensable role. Their primary functions include:
- As a template or stabilizer:During the synthesis of nanoparticles, adsorption onto the particle surface is utilized to prevent agglomeration and control their size and morphology through steric hindrance or electrostatic repulsion.
- Forming micelles as carriers:When surfactants reach their critical micelle concentration, the micelles formed have a hydrophobic core that can encapsulate poorly soluble drugs or functional molecules, enabling solubilization and targeted delivery.
Regarding safety considerations, particular attention must be paid in pharmaceutical and cosmetic applications.
- Biocompatibility:Choose natural or low-irritant surfactants (such as lecithin, sucrose esters, poloxamers) to avoid causing hemolysis or cytotoxicity.
- Fate in the Body: Consider the metabolism, degradation, and excretion pathways of surfactants in the body to ensure that both the surfactants and their degradation products are non-toxic and harmless.
- Regulatory Compliance: Compliance with regulations and limits on surfactant use in relevant fields (such as pharmaceuticals, cosmetics, and food) must be strictly followed.